The sound of squeaking plastic parts is a minor irritant as the black cab surges into a sharp corner, its body leaning heavily.

Normally, at high speed, the rattling would have been drowned out by a rumbling, whining diesel engine But this taxi is different.

This is the first hydrogen-powered London cab, developed to showcase zero exhaust emission vehicles during the 2012 London Olympics.

The taxi has been put together by Lotus, a UK company more famous for its Formula 1 team and for making sports cars such as the Elise.

Long-range electric motoring.

From the outside, the taxi looks like any other black cab and it weighs as much too – a whopping 2.6 tonnes.

But driving it at the Lotus test track in Norfolk feels completely different as it accelerates from 0-60mph (0-100km/h) in 15.5 seconds – slow compared with most cars, but a full seven seconds quicker than an ordinary black cab.

Under the taxi’s familiar exterior – within its generous bulk – the truly special bits are hidden.

The back wheels of the taxi are powered by two electric motors – though it is not an electric car in the conventional sense of the term.
Dr Ashley Kells, programme manager at Intelligent Energy Dr Kells says fuel cells deliver electricity, similar to the way a battery does

Yes, the taxi has a lithium polymer battery that delivers electricity to the electric motors, but this is not its main source of power.

The cab also has a stack of fuel cells that convert energy from hydrogen, which is stored in a tank under the car’s bonnet, into electricity.

The electric motors can be powered by either the fuel cell system, or by the battery, or by a combination of the two.

During braking the battery, which is located in the middle of the taxi under the floor of the cabin, is recharged by two sources:

* surplus electricity created by the fuel cells is sent to the battery
* kinetic energy captured during braking is sent to the battery from the back wheels, via the electric motor.

With two different power sources – fuel cell system and battery – the taxi could be described as a hybrid vehicle, but again, not in the conventional sense of the term, which usually refers to petrol-electric hybrids.

How the Taxi works.

1. The taxi is powered by a stack of fuel cells that get their fuel from a hydrogen gas tank under the bonnet
2. The fuel cells convert the energy stored in the hydrogen into electricity, which drives two electric motors that drive the two back wheels
3. The electricity stored in the battery is then used to supplement the electricity from the fuel cells to propel the car forward
4. During braking, the energy from the fuel cells is not needed so it is instead channelled into a battery. The battery also gets energy from the wheels during braking